Insulin‐mediated Akt/eNOS signaling is defective in ob/ob mouse aorta due to negative regulation by translocated GRK2

We investigated whether and how, in aortas from ob/ob mice (a model of type 2 diabetes), translocation of G‐protein coupled receptor kinase 2 (GRK2) to membranes regulates insulin‐induced relaxation and NO production. Endothelium‐dependent relaxation was measured in aortic rings. The expression and activities of GRK2, β‐arrestin2, and Akt/eNOS proteins were assayed by Western blotting. In ob/ob aortas [vs. control (Lean) aortas]: (a) insulin‐induced relaxation and NO production were reduced, the ob/ob vs. Lean differences being abolished by Akt‐inhibitor (due to reductions in the Lean group); (b) these deficits were prevented by GRK2‐inhibitor; (c) insulin‐stimulated Akt and eNOS phosphorylations were, or tended to be, decreased (in the membrane fraction, some were markedly decreased); (d) GRK2 protein in membranes was elevated, and was further increased by insulin. In ob/ob aortic membranes, insulin increased GRK2 protein and decreased β‐arrestin2 protein, and the phosphorylation levels of Akt (at Thr 308 ) and eNOS (at Ser 1177 and Thr 495 ) under insulin were augmented by GRK2‐inhibitor. This study identifies GRK2 translocation as a key negative regulator of insulin responsiveness in the murine aorta. GRK2 may be an important regulator of the β‐arrestin2/Akt/eNOS signaling pathway, which is implicated in diabetic endothelial dysfunction.